The possibility of noninvasive biochemical analysis provided by the measurement of the spectra of phosphorous and other nuclei has motivated the increasing use of high field superconducting magnets in Magnetic Resonance Imaging (MRI) systems. A significant fraction of the operating cost of a superconducting MRI system is associated with the consumption of cryogens used to cool the magnet. Present cryostats use liquid helium and liquid nitrogen in an open-cycle mode; cooling is achieved by boiling off the cryogens and venting the gases to the atmosphere. There is a strong need for a reliable and efficient closed-cycle cryocooler that would eliminate the consumption of cryogens and hence reduce the cost and simplify the operation of superconducting MRI systems. A novel concept for providing active cryocooling to superconducting MRI systems was developed and evaluated during Phase I of this research project. The objective of the proposed Phase II is to develop the necessary hardware to demonstrate the thermodynamic performance and establish the manufacturing costs of the proposed cryocooler. The principal components to be designed, fabricated, and tested during Phase II include a miniature gas-bearing turboexpander and a high effectiveness thermal radiation shield system. These components, along with a commercially available compressor will be assembled into a working prototype and tested under actual operating conditions. In Phase III, this prototype will be incorporated into a commercial MRI facility.